Waste lubricating oils include used motor oil, diesel oil, crankcase oil, transmission oil, and the like, usually collected from gasoline service stations. These waste oils contain a number of contaminants arising both from their use and from additives added prior to their use. These contaminants, for the most part, include calcium, barium, zinc, aluminum and phosphorus arising from detergent dispersant agents, iron from engine wear, lead and light end hydrocarbons from gasoline, and water. In order to reuse these oils, the contaminants must be substantially removed.
Due to the high viscosity of the oil, the fine colloidal or dissolved form of the contaminants and the dispersing nature of the additives, the contaminants cannot be removed by a simple filtration procedure without some preliminary treatment.
The most widely used process for upgrading waste oils is the acid-clay process. In accordance with this process, waste oil is contacted with high strength sulphuric acid and the contaminants are removed in an acid sludge. The oil is thereafter contacted with a decolorizing clay to absorb additional contaminants and color bodies.
There are a number of problems associated with this process. Firstly, the process produces large amounts of acid sludge which must be disposed of. Secondly, large volumes of corrosive acid are consumed by the process. Thirdly, up to 20% of the original waste oil is lost with the acid sludge.
Other methods have been proposed for reprocessing waste oil by obtaining a metathesis reaction with the contaminants by adding an aqueous solution of pretreatment chemicals, which precipitates the metals to render them phase separable from the oil. In U.S. Pat. No. 3,930,988 issued to M. Johnson, waste oil is contacted with an aqueous solution of ammonium sulphate and/or ammonium bisulphate to precipitate the metals into an aqueous phase, separable from the oil base. In U.S. Pat. No. 3,879,282, also issued to M. Johnson, waste oil is contacted with an aqueous solution of one or more of triammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate. In U.S. Pat. No. 4,204,946 issued to the present inventor, waste oil is contacted with an aqueous solution of ammonium sulphate and aluminum sulphate. In all of the above processes, the pretreatment chemicals are added to the waste oil in an aqueous solution and the metals are separated in an aqueous phase. Also, the temperature of the reaction is limited to about 200.degree.-500.degree. F. High temperature treatments have generally been avoided when reprocessing waste lubricating oils to avoid cracking of the oil.
In U.S. Pat. No. 4,151,072, issued to M. Johnson, a process is described for reprocessing waste oil wherein the oil is contacted with an aqueous solution of an ammonium salt such as ammonium phosphate. The temperature of the oil is raised gradually through one or more contacting vessels to a final temperature of less than about 400.degree. F. to initially achieve a phosphate replacement reaction with the contaminants, and to remove water and light hydrocarbons. The oil is then filtered using a filter aid. It should be noted that the above process again requires that the pretreatment chemicals be added in an aqueous phase, and the temperature of reaction be limited to about 140.degree.-390.degree. F.